An overheat potential exists by the feeding of narrow width medium (less than 8.5 inch, which is full size, standard paper in the United States) through a fuser in a paper feed system that uses one edge of the paper as a position margin, as opposed to the center of the paper. The thermal problem is caused by the accumulation of more thermal energy on that portion of the fuser hot roller which does not contact the paper when it is fed through the fuser. This can result in the fuser elements exceeding safe operating temperature (overheating), resulting in melting or other physical destruction of the imaging apparatus.
One existing prior art solution when the paper edge is the feeding boundary or reference is to maintain a count of envelopes and slow the throughput from 10 pages per minute (10 ppm) to 5 ppm by increasing the interpage gap when 15 envelopes are printed consecutively from the last idle condition. The envelope count is reset to zero if the printer is idle long enough for the fuser temperature, as measured by a thermocouple or other sensor, to drop to the standby temperature. Only printing of consecutive envelopes results in the slowing of throughput. Combinations of other substrates are printed at the maximum throughput of the printer.
Japanese patent 57-102676, dated Jun. 25, 1982, addresses the overheating by sensing the heating roller where the short-width paper does not extend and disconnecting the fuser heater when an predetermined upper limit is sensed.
Another existing prior art, in which the paper edge is the feeding boundary or reference, employs a sufficiently thick aluminum layer in the hot roller and slowing the rate for envelopes from 8 ppm to 6 ppm by enlarging the interpage gap (gap between two successively printed media). The thicker aluminum adds to cost and increase warm-up time.